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  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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<body>
  <script>
    // 函数的返回值要用return
    function fu() {
      return 20;
    }

    // 小括号才是调用者
    let result = fu();
    console.log(result);
  </script>
</body>

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